Green tea is a popular beverage which has been consumed in China and Japan for many hundreds of years. Recently, extensive laboratory research and epidemiologic studies have shown that compounds present in green tea (particularly the catechins) may reduce the risk of a variety of illnesses. These studies, along with the increasing complexity of the consumer's palate has led to increased consumption of green tea, even in markets (such as the USA and Western Europe) where there is no tradition of green tea consumption.
The aroma of green tea is seen as an important indicator of quality. There have been many investigations into the compounds responsible for particular odours of green tea and it is conventionally held that E-2-hexenal, in particular, is characteristic of the undesirable “green note” of low-grade teas, whilst linalool is characteristic of the aroma of high grade teas.
K. Yamaguchi and T. Shibamoto (J. Agric. Food Chem., 1981, 29, pp. 366-370) studied the volatile components of Gyokuro (a high grade green tea) and showed that linalool was a major component thereof whilst E-2-hexenal was only present in very low amounts.
M. Shimoda et al. (J. Agric. Food Chem., 1995, 43, pp. 1621-1625) studied the contributors to the odours of different grades of green tea and their relationship to the odours of their infusions. Linalool was found to contribute to floral and fruity aromas while E-2-hexenal was said to give a green and sickening odour. High grade Sen-cha contained only trace amounts of E-2-hexenal and had a significant amount of linalool, whilst low-grade sencha comprised approximately 71 μg/kg of linalool and 15 μg/kg E-2-hexenal.
M. Kato and T. Shibamoto (J. Agric. Food Chem., 2001, 49, pp. 1394-1396) studied a range of green teas and found that the relative level of linalool is higher in high-quality tea than in low-quality tea. Furthermore, an appreciable amount of E-2-hexenal was found in low-quality tea but not in high quality tea.
JP 2002-330698 A (KOJIMA MAKOTO) discloses a method capable of collecting inherent grassy-smelling flavor components of green tea. The method comprises leading an exhaust gas discharged from a firing dryer in the finish processing step of raw tea leaves. The inherent grassy-flavor components of green tea can be added to green tea beverage products by using the obtained condensed tea flavor component-containing product. There is no disclosure, however, of E-2-hexenal or linalool. Furthermore, by the time that fresh leaves are fired in the finish processing step of green tea manufacture, they have already been dried to a moisture content of much less than 30% (see, for example, “Tea: Cultivation to Consumption”, K. C. Willson and M. N. Clifford (Eds), 1st Edn, 1992, Chapman & Hall (London), Chapter 13, p. 422). Thus much of the E-2-hexenal will already have been lost before the tea leaves reach the firing dryer.
Surprisingly, we have found that adding an aroma composition relatively high in E-2-hexenal to a green tea product actually enhances the aroma of the green tea product. The resulting green tea products were found to have a relatively high content of E-2-hexenal and yet have an aroma enriched in floral and citrus notes and reduced in the green notes typical of low-quality teas.
Tests And Definitions
Beverage
As used herein the term “beverage” refers to a substantially aqueous drinkable composition suitable for human consumption.
Tea
“Tea” for the purposes of the present invention means material from Camellia sinensis var. sinensis and/or Camellia sinensis var. assamica. 
“Tea leaf” for the purposes of this invention means a tea product that contains one or more tea origins in an uninfused form.
“Fresh tea leaf” refers to tea leaf that has never been dried to a water content of less than 30% by weight, and usually has a water content in the range 35 to 90%.
“Leaf tea product” refers to tea leaf that has been dried to a moisture content of less than 30% by weight, and usually has a water content in the range 1 to 10% by weight (i.e. “made tea”). The leaf tea product of this invention is a beverage precursor that is in a form suitable for directly preparing a beverage, e.g. by contacting the leaf tea product with an aqueous medium such as boiling water or cold water. The leaf tea products of this invention are preferably packaged. The leaf tea products may be packaged in an infusion package (e.g. tea bag) and/or an air tight envelope such as a foil bag.
“Fermentation” refers to the oxidative and hydrolytic process that tea undergoes when certain endogenous enzymes and substrates are brought together, e.g., by mechanical disruption of the cells by maceration of the leaves. During this process colourless catechins in the leaves are converted to a complex mixture of yellow and orange to dark-brown polyphenolic substances. “Green tea” refers to substantially unfermented tea.
By “ready-to-drink tea” is meant a beverage comprising tea solids. Ready-to-drink tea usually has a water content of at least 80%, optimally between 85 and 99.9% by weight. Ready-to-drink tea may be packaged in an air tight container such as a can or bottle. The tea solids content of ready-to-drink tea is typically in the range of 0.001 to 5% by weight, preferably 0.01 to 3% by weight and most preferably 0.1 to 1% by weight.
Total Organic Carbon
The total organic carbon (TOC) content of an aroma composition is a measure of the total concentration of aroma compounds in the composition. Analysis of TOC is based upon a combustion method.
The TOC measurements were made using a Shimadzu TOC-V Carbon Analyser, an automated system that analyses aqueous samples for Total Carbon (TC) and Total Inorganic Carbon (TIC). The combustion tube is filled with platinum catalyst and heated to 680° C. Carrier gas (purified air) is supplied to this tube. A sample is injected and all the carbon oxidised to CO2 which is measured using an infra-red analyser.
TOC is measured by using a ‘by difference’ method whereby Total Carbon (TC) and the Total Inorganic Carbon (TIC) of a sample are measured, the difference being the Total Organic Carbon (TOC). The aroma compositions do not contain inorganic carbon and therefore the TC data has been used as a direct measure of TOC.
Determination of Aroma Compounds
The amounts of the various aroma compounds in aroma compositions and green tea products are determined by headspace gas-chromatography.
Sample Preparation for Aroma Compositions
For aroma compositions with a high TOC, the composition may separate into at least two phases on storage. Thus the composition should be homogenised, e.g. by shaking and/or stirring, prior to analysis.
If the TOC of the aroma composition is more than 25 ppm, it should be diluted in de-ionised water (20° C.) to give a TOC of 25 ppm.
Sample Preparation for Ready-to-Drink Tea
Ready-to-drink tea is analysed without any dilution.
Sample Preparation for Leaf Tea Products
A portion of the leaf (2.00 g) is placed in a vacuum flask. Freshly boiled Highland Spring™ mineral water (200 ml) is added, the flask sealed and then gently swirled for 5 seconds to mix the infusion. The flask is left for 3 minutes after which it is gently swirled once more for 5 seconds. After 4 minutes the infusion is emptied from the flask and the leaf removed by filtration through a double layer of muslin. The infusion is then collected in a bottle, capped and cooled in cold water to room temperature (20° C.).
Analysis
Samples (10.0 g) are placed in headspace vials, capped and analysed using a Perkin Elmer GC fitted with a HS40XL headspace auto sampler and a cryo-focussing unit. The sample of headspace is taken after the sample is incubated at 65° C. for 20 minutes. The headspace sample is then transferred to the GC which is fitted with a Carbowax™ column. External standards are used to monitor the performance of the headspace autosampler and retention times on the GC column.